Etch system with integrated inductive coupling

ABSTRACT

An integrated capacitively-coupled and inductively-coupled device is provided for plasma etching that may be used as a primary or secondary source for generating a plasma to etch substrates. The device is practical for processing advanced semiconductor devices and integrated circuits that require uniform and dense plasma. The invention may be embodied in an apparatus that contains a substrate support, typically including an electrostatic chuck, that controls ion energy by capacitively coupling RF power to the plasma and generating voltage bias on the wafer relative to the plasma potential. An etching electrode is provided opposite the substrate support. An integrated inductive coupling element is provided at the perimeter of the etching electrode that increases plasma density at the perimeter of the wafer, compensating for the radial loss of charged particles toward chamber walls, to produce uniform plasma density above the processed wafer. The device has a capacitive coupling zone in its center for energizing etching ions and an inductive coupling zone at its perimeter of the wafer. Both zones together with plasma create a resonant circuit with the plasma.

This application is a Continuation-in-Part of U.S. patent applicationSer. No. 10/716,729, filed Nov. 19, 2003, hereby expressly incorporatedherein by reference herein.

FIELD OF THE INVENTION

This invention relates to high density plasma generating devices,systems and processes, particularly for the manufacture of semiconductorwafers and integrated circuits. This invention particularly relates tothe high density inductively coupled plasma (ICP) and capacitivelycoupled plasma (CCP) sources used in semiconductor and integratedcircuit processing.

BACKGROUND OF THE INVENTION

There are two principal groups of the plasma sources:capacitively-coupled plasma sources, which utilize RF electric fieldcoupling to the plasma, and inductively coupled plasma (ICP) sources,which utilize RF magnetic field coupling to the plasma.

Capacitively-coupled plasma sources include “planar diode” or “parallelplate” systems, in which a surface to be etched is placed on oneelectrode that is coupled to an RF generator through a blockingcapacitor, which does not allow real current to flow from the electrodeto the RF generator. This forces the plasma to find a condition in whichthe electron current reaching the electrode from the plasma exactlybalances the ion current averaged over one RF cycle. Since electrons aremore mobile than ions, the electrode acquires a negative potential tolimit the electron current and encourage the positive ion current. Thisnegative potential is called the self-biased voltage, which results inan energetic ion bombardment of the surface being etched. Changingapplied RF power can control the ion bombardment. A planar triodecapacitively-coupled plasma system with two RF electrodes and groundedwalls represents another geometry.

Capacitively-coupled sources have widespread use in semiconductor plasmaprocessing, but have some problems and limitations. For instance, theelectrical behavior of a capacitively-coupled discharge is influenced bythe reactor geometry, where plasma potential depends strongly on thearea of the powered electrode relative to the area of all other surfacesin contact with the discharge. In symmetrical systems, both electrodescan be subjected to high-energy ion bombardment, including energetic ionbombardment of walls and fixtures causing sputtering of these surfacesand chamber contamination. The pressures typically used have to bemaintained high enough (>100 mTorr) so that sputtering of the groundedsurfaces is not a problem. In asymmetric low pressure systems, only thebiased electrode is sputtered, as the walls are exposed to low energyions, and a nonuniform plasma density that peaks in the center isproduced. Non-uniform plasma caused by large losses of electrons andions to the chamber walls causes nonuniform etch rates to result.Optimal geometry at low pressure has been cylindrical geometry,including that in hexode systems, which is not adaptable to 300 mmsingle wafer semiconductor manufacturing.

A common drawback of the above-described systems is an inability toindependently control ion energy and ion flux at a fixed pressure and RFfrequency. Planar triode systems solve this problem but requirerelatively high pressure to eliminate sputtering of the top electrode,which voltage can be reduced by increasing frequency at the topelectrode and decreasing frequency at the wafer electrode. In the VHFfrequency range, high plasma densities can be generated with low appliedvoltages. Higher frequencies result in less damage, more uniformityacross the electrode, and the ability to process larger substrate areasat more uniform rates. For example, recent developments in capacitivelycoupled plasma systems step in the direction of higher excitationfrequencies in the 30 to 300 MHz range, where high plasma densities canbe generated with low applied voltages. This produces a lower damageprocess with improved uniformity across the electrode, so that largerareas may be processed at more uniform rates.

Inductively coupled plasma (ICP) sources provide relatively low ionenergy bombardment and reasonable etch rates. Common ICP sources includecoils having planar, cylindrical or dome-shaped geometries. Theso-called helical resonator is a cylindrical ICP source in which amovable tap on the coil is used to optimize tuning and power transferinto the plasma. The helicon source is an ICP source that uses anantenna with specific geometry to launch a wave along an externallyapplied magnetic field, which can couple energy into the plasmaelectrons. High frequency (2.45 GHz) electromagnetic radiation is alsoused to generate high-density plasma in the microwave range butexcitation is limited to <10¹¹ electrons per cm³, so it is mostly usedas downstream plasma for wafer processing. In combination with largemagnetic fields (875 Gauss for excitation at 2.45 GHz) an electroncyclotron resonance (ECR) can be achieved with which plasma densities inthe 10¹³ cm⁻³ range. There are many commercially available plasmasources that can be used to generate high-density plasmas (>10¹¹electrons cm⁻³) at relatively low pressures (<10 mTorr) withoutrequiring the application of high voltages.

Plasma sources are used in combination with a capacitively-coupled,RF-powered electrode on which the processed wafer is placed. Such anelectrode is often an electrostatic chuck (ESC), which consists of abase plate having cooling channels or heating structure inside andconnections for backside gas, DC chucking electrodes, and temperaturedetectors, etc. Tn some cases a flexible bellows mounted between arobust backside flange and a bottom chamber flange allows verticalmovement of the ESC to enhance process control variables.

In systems with independently RF biased substrate holders, independentcontrol of the ion energy and ion flux can be obtained. Typically, thepower used in the high-density plasma source is much larger than thebias power applied to the wafer-bearing electrode. Increasing the biaspower increases the ion energy without changing the ion current density.Increasing the source power results in both an increase in the ion fluxand a decrease in the ion energy.

Etch uniformity at the wafer is affected by ion flux and ion energy.Generally, the ion flux towards the wafer is a function of plasmadensity distribution. To achieve uniform etching, uniformly distributedplasma parameters have to be provided. Typically, the TCP sources withspiral coils produce a plasma distribution with a peak at its center atthe pressures that are typically used. Multiple coil configurations,magnetic fields, wafer pedestal size and material, and additionalchamber hardware are used to improve plasma density distribution. Forinstance, multipolar magnetic field confinement of a plasma helps toincrease plasma density and improve plasma homogeneity, but only forpressures well below 1 milliTorr (mTorr). From these pressures, plasmahomogeneity degrades rapidly as the pressure is increased. Anothersolution has been to provide a magnetic confinement ring around anelectrostatic chuck to confine the plasma within the area defined by thering. Unfortunately, the magnetic confinement ring often produces thewell-known cusp effect on the peripheral surface of the wafer due to themagnetic field of the confinement ring.

In ICP systems, the use of dual coils or dual zone coil configurationswithin an ICP source can partially improve the plasma densitydistribution. However, because of the distance of the coil from thewafer pedestal, increased RF power is required to compensate radialpower loss, for which an additional RF generator and matching unit aretypically needed. Still, the sidewall effect is not completely removedfrom the wafer. Significant chamber modifications may be required. Alarger size dielectric windows may be needed, and the window thickenough to withstand atmospheric forces. Additional controlling units andcooling may be required. For current 300 mm size wafers, all thesecomponents represent large and expensive consumable parts, increasedcomplexity, resulting in high cost of operation and significantly highoverall cost of the machine.

Furthermore, producing uniformly distributed plasma over a wafer mayhave the undesirable effect of reducing plasma density. A wafer exposedto the reduced plasma density generally takes more time to produce adesired etch or deposition than a wafer subject to a higher plasmadensity. Hence, the etch or deposition process may take longer tocomplete in a uniformly distributed plasma environment.

Accordingly, there is a need for an ICP source that produces a highdensity uniform plasma that is simple and low in cost.

SUMMARY OF THE INVENTION

An objective of the present invention is to provide a plasma source forutilization in a plasma process, such as plasma etching, plasmadeposition or plasma cleaning, that is uniform across the surface of thesubstrate being processed. Another objective of the invention is toprovide a compact plasma source that can be used either as primaryplasma source or as complimentary source to a primary JCP source. Afurther objective of the invention is to provide a highly effectiveplasma source for a simplified reduced cost chamber.

According to principles of the present invention, a compact, integratedCCP and ICP plasma source is provided. In certain embodiments, anelectrostatic, inductively-coupled wafer support (i-ESIC) is provided inthe vacuum chamber of a plasma processing apparatus. The i-ESIC wafersupport has two integrated portions, including a central wafer supportsurface that is capacitively coupling to the plasma, and an inductiveionization source that is connected to the central surface and providesinductively-coupled RE energy to the plasma.

In certain illustrated embodiments, the capacitively-coupled centralwafer support surface is an electrostatic chuck (ESC), which holds awafer during processing. The chuck is preferably biased to a negativepotential relative to the plasma to control the energy of ions from theplasma onto the supported substrate. The inductively-coupled componentis preferably annular and surrounds the central portion, coupling energyto the plasma through RF magnetic fields generated by an inductiveelement therein.

In one embodiment, the central substrate support surface and the annularinductive element are coupled in series between the chamber ground andan RF generator through a matching network. For example, the centralsupport may be capacitively-coupled to the matching network andcapacitively-coupled to the inductive element, which, in turn, may becapacitively-coupled to ground. The impedances of the series circuit maybe designed in conjunction with those of the matching network to producea single resonant circuit. Alternative configurations are describedbelow.

According to certain principles of the present invention, the integratedwafer chuck and active peripheral ionization source is provided. Withthe source, plasma is generated in the vicinity of the wafer where itwill affect immediately the plasma distribution above the wafer. Becauseof the close proximity of the source to the wafer, the source does notrequire a large RF power supply. The source may be used as a secondaryor complementary source with which plasma is generated that compensatesfor non-uniformity generated by a primary ICP source. The source of thepresent invention generates a higher density plasma that diffuses into alow-density capacitively-coupled plasma above the wafer. With thepresent invention, RF hardware can be reduced in size and power. Thesource may be used as a single integrated plasma source sufficient toprocess wafers placed on the pedestal, which may be, for example, anelectrostatic chuck (ESC).

An alternative embodiment of the invention includes a substrate supportthat provides control of ion energy due to capacitive coupling of RFpower to the plasma and a voltage bias on the wafer with respect to theplasma potential. An upper electrode is also provided that is RF-biased,and may be biased with a different RF frequency, typically higher, thanthe substrate support, and which provides enhanced plasma production. Inthis embodiment, the upper electrode includes an integrated inductivelycoupled element at its perimeter that provides increased plasma densityat the perimeter of the upper electrode. When the electrode distancefrom the substrate support is comparable to the diameter of the wafer,the upper electrode compensates for radial loss of charged particlestowards the chamber walls and thus improves plasma density uniformity inthe vicinity of the processed wafer. The integrated CCP and ICP upperelectrode can be used in combination with an ESC wafer support, or withan integrated-ESIC device described in the embodiments above.

An integrated-ESIC device, an integrated upper electrode device or acombination of both, can operate simultaneously in two modes. Bycapacitively coupling at the center of the integrated device and byinductive coupling at the perimeter of the device.

Preferably, both the CCP and CP components of the device are adjusted tocreate resonant circuit in combination with plasma itself.

The present invention is based, in part, on the principles that etchuniformity at a wafer is affected by plasma density distribution and byion energy, and that to achieve uniform etching, uniformly distributedplasma parameters should be provided. It has been found that it is notsufficient to reduce the loss to the walls only in a passive way, andthat the most effective way to reduce loss to the walls is to generatean active plasma in the depleted region around the wafer. Plasma densityabove the wafer is most easily affected by plasma generation in thevicinity of the wafer. This is done by using ICP, which leads tohigh-density plasma generation. This approach does not require oversizedRF power supplies. The present invention utilizes existing RF generatorsto bias a wafer pedestal. A center-peaked plasma distribution that isgenerated by the remote primary ICP source may be compensated for at thewafer edge by peripheral plasma generation from a secondary high-densityplasma source according to the present invention.

Advantages of the integrated CCP and ICP device in combination with anESC include high density-plasma production at perimeter of the wafer,compensation of non-uniformity in plasma density that is usually in theform of a peak at the center of the chamber, uniform plasma processingat the wafer. The advantages also include a compact integrated devicethat provides simultaneous and independent ion energy and ion fluxcontrol, combined capacitive aid inductive coupling in one device, and adevice that is suitable for etching, deposition, sputtering and cleaningtechnology. The source of the present invention eliminates the need forlarge and robust dielectric windows while increasing dielectric windowlifetime and reducing window failure and window cleaning

These and other objectives and advantages of the present invention willbe more readily apparent from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic cross-sectional view of a plasma processingapparatus embodying principles of the present invention.

FIG. 1A is a diagrammatic cross-sectional view, similar to FIG. 1, of analternative embodiment of a plasma processing apparatus according toprinciples of the present invention.

FIG. 2 is a perspective diagram, partially cut away, illustrating oneembodiment of an integrated, electrostatic, inductively-coupled wafersupport of the apparatus of FIG. 1, according to one embodiment of theinvention.

FIG. 2A is an enlarged perspective view of a portion of one embodimentof a shield of the integrated, electrostatic, inductively-coupled wafersupport of FIG. 2.

FIG. 3 is an circuit diagram of an integrated CCP and ICP device of theplasma processing apparatus embodiments of FIGS. 1 and 1A.

FIGS. 3A-3F are cross-sectional diagrams of six exemplary coils that canbe used for the inductively-coupled element of the wafer supports ofFIGS. 1 and 2.

FIGS. 4A-4B are top and perspective diagrams, respectively, of oneembodiment of a bifilar coil similar to that of FIG. 3F.

FIGS. 4C-4D are top and perspective diagrams, respectively, similar toFIGS. 4A-4B, of another embodiment of a bifilar coil.

FIGS. 5A-5C are perspective diagrams of one embodiment of an inductiveelement, a graph of time-averaged RF electromagnetic energy for suchelement, and a graph of power density delivered into the plasma by suchelement.

FIGS. 6A-6B are top and perspective diagrams, respectively, of anotherembodiment of an inductive element for the wafer support of FIGS. 1 and2.

FIG. 6C is a graph of time-averaged RF electromagnetic energy for theelement of FIGS. 6A and 6B.

FIG. 6D, is a slot pattern diagram for a Faraday shield for use with theelement of FIGS. 6A and 6B.

FIG. 6E is a graph of time-averaged RF electromagnetic energy for theelement of FIGS. 6A and 6B equipped with a Faraday shield having theslot pattern of FIG. 6D.

FIG. 7 is a disassembled perspective view of an alternative embodimentof the wafer support of FIGS. 1 and 2 that employs a segmentedperipheral source for the inductive element.

DETAILED DESCRIPTION

As illustrated in FIG. 1, according to one embodiment of the invention,a plasma processing apparatus 10 includes a vacuum processing chamber 11enclosed in a chamber wall 12. An integrated, electrostaticinductively-coupled device or wafer support (i-ESIC) 20 is mounted inthe chamber 11 to support individual wafers 14 thereon for processing bya plasma 15 maintained within the vacuum chamber 11.

Referring to FIGS. 1 and 2, the wafer support 20 has two integrated maincomponents or portions: a capacitive-coupling component 21, whichprovides a capacitively-coupled RF path to a plasma 15, and aninductively-coupled component 22, which provides an inductively-coupledRF path to the plasma 15. The capacitively-coupled component 21 is acentral substrate support portion, typically an electrostatic chuck(ESC), which holds individual wafers to the support 20 duringprocessing. The chuck of the central portion 21 also provides control ofthe energy of ions from the plasma by capacitively coupling RF power tothe plasma 15 and generating a voltage bias on the wafer 14 with respectto the plasma potential. The inductively-coupled component 22 is annularand surrounds the central portion 21, providing coupling to the plasmathrough RF magnetic fields generated by an inductive elementincorporated within annular portion 22.

The i-ESIC wafer support 20 is compact and includes the central portion21 and the perimeter portion 22. The central portion 21 of the substratesupport 20 serves as a support for a wafer 14, holding and releasingwafers according to principles known in the field of ESC manufacturingand applications. The central portion 21 can contain one or both of aheating device and a cooling device (not shown) to sustain wafers 14 atprocess temperature, and other sensors and instrumentation (also notshown) used in such devices. Internal structure of the ESC is well knownto those familiar with the field. The substrate support 20 is biasedthrough a capacitor 16 and a matching network 17, which are connected inseries between the support 20 and an RF power supply 18.

The peripheral portion 22 has an inside diameter that is larger than thediameter of the wafers 14 that are to be processed on the support 20.The peripheral portion 22 includes an annular inductive device 23 havingan inner end 23 a connected through an impedance 24 to the centralportion 21, and an outer end 23 b connected through an impedance 25 to abottom chamber shield and support flange 26, which is grounded via thechamber walls 12. The central portion 21 is supported on, and insulatedfrom, the support flange 26 by an insulator ring 31. The inductivedevice 23 has a relatively low inductance (less than 1 micro-Henry) andis schematically shown in FIG. 1 supported on the support 20 in aninsulating envelope 27. The envelope 27 may be formed of Al₂O₃ or othersuitable dielectric, which insulates the inductive device 23 from thebottom shield 26. The grounded bottom shield 26 electrically shields thedevice 20 to prevent plasma ignition below the support 20.

The top surface 23 c of the inductive element 23 is protected from theplasma 15 by a metallic shield 28. Shield 28 serves as a Faraday shieldand is made of an electrically high-conductivity material such as metal.To provide transparency to RF magnetic fields, the shield 28 containsradially or almost radially extending slots 29 that overlap the width ofthe inductive element 23. Generally, the slots 29 of the shield 28 areoriented in parallel or almost parallel to the flux lines of the RFmagnetic field generated by the inductive element 23. The number anddimensions of the slots 29 are not critical and can vary, but arelatively low number of slots will provide operation of inductivedevice 23 as an ICP source in an ICP mode. To achieve good azimuthaluniformity, a minimal number of slots should be at least N>=π/(2 arctan(d/2D), where d is the width of the annular inductive element 23 and Dis the diameter of an annular inductive element 23. In the illustratedembodiments, N is approximately 12. Above a certain number of slots, forexample 60 to 80, which might exist for inductive elements 23 havingdiameters of from 300 to 400 mm, the performance of the element 23 as anICP source is not strongly affected by increasing the number of slots29. Typical and preferable slot width is in the range of 0.5-5 mm,although the acceptable range of slot width is not limited by thisinterval.

The electrostatic shield 28 functions to protect the inductive element23 from the plasma 15, (e.g. from the direct heating, erosion,sputtering of the surface, contamination or conductive deposits) and toprovide effective ICP operation. One example of a preferredconfiguration of slots 29 for the shield 28 is shown in the FIG. 2A.Overlapping portions 29 a of the slot structure eliminate directdeposition on the inductive element 23. Other slot configurations, suchas slots 29 of chevron-shaped cross-section, might also be preferable.

As described and illustrated above, the wafer support 20, together withinductive device 23, is compact. The inductively-coupled member 22 ofthe support 20 provides increased density at the perimeter of the wafer14, and thus compensates for radial loss of charged particles towardsthe walls 12 of the chamber 11, and generates plasma 15 of uniformdensity above the wafer 14 being processed. The i-ESIC device operatescontinuously in two modes: a capacitive-coupled plasma (CCP) mode in thecenter of the device 20 where the wafer 14 is supported, and aninductively-coupled plasma (ICP) mode at the perimeter of the wafer 14,both modes being powered utilizing a common matching network 17 and RFgenerator 18.

FIG. 1A illustrates tn alternative embodiment 100 of the plasmaprocessing apparatus 10 that is more adaptable to etch systems. Theapparatus 100 may include vacuum processing chamber It enclosed inchamber wall 12. The integrated, electrostatic inductively-coupleddevice (i-ESIC) 20 of FIG. 1 may be mounted in the chamber 11 to supportindividual wafers 14 for processing, or a wafer holder may be providedthat only includes the capacitive-coupling wafer support component 21 onwhich is supported the wafer 14, but includes no IC component 22.

In the embodiment 100 of FIG. 1A, an integrated device 120 is providedfacing the wafer support 21, which includes a central electrode 121 thatprovides a capacitively-coupled RF path to a plasma 15. The device 120also includes an inductively-coupled component 122 that provides aninductively-coupled RF path to the plasma 15. The capacitively-coupledcomponent 121 is a central electrode portion for energizing the plasma15 for etching a wafer 14 on the support 21. The central portion 21 ofthe electrode provides control of the energy of ions from the plasma bycapacitively coupling RF power to the plasma 15 and generating a voltagebias of the plasma with respect to the wafer 14 on the support 21. Theinductively-coupled component 122 is annular and surrounds the centralelectrode portion 121, providing coupling to the plasma through RFmagnetic fields generated by an inductive element incorporated withinannular portion 122.

The integrated device 120, with or without an i-ESIC wafer support 20,including the central electrode 121 and the perimeter portion 122, iscompact. The central electrode 121 of the device 120 is biased through acapacitor 116 and a matching network 117, which are connected in seriesbetween the electrode 20 and an RF power supply 118.

The peripheral portion 122 has an inside diameter that can be largerthan the diameter of the wafers 14 being processed. The peripheralportion 122 includes an annular inductive device 123 having an inner end123 a connected through an impedance 124 to the central portion 121, andan outer end 123 b connected through an impedance 125 to the groundedchamber walls 12 or the grounded chamber lid 112. The electrode 121 issupported by the integrated device 120 on the chamber lid 112, but isinsulated from the lid 112 and the chamber wall 12. The inductive device123 has a relatively low inductance (less than 1 micro-Henry).

A dielectric window 123 c may be provided at the bottom side of theinductive device 123, allowing the inductive device 123 to be locatedoutside of the vacuum chamber 12. The bottom of the inductive device 123or of the dielectric window 123 c may be protected from the plasma 15 bya metallic shield 128 that is similar to the shield 28, described above,and serves as a Faraday shield. This shield 128 may be made of anelectrically high-conductivity material such as metal, and can be madetransparent to RF magnetic fields by providing radially, or almostradially, extending slots.

The electrostatic shield 128, where used, would function to protect theinductive element 123 or window 123 c from the plasma 15 and to provideeffective inductive coupling of energy from the inductive element 123into the chamber 11. Like the wafer support 20 described above, theintegrated device 120, with the CCP electrode 121 together withinductive device 123 of the peripheral portion 122 is a compact devicethat provides increased plasma density at the perimeter of the wafer 14,which can compensate or radial loss of charged particles towards thewalls 12 of the chamber 11, providing plasma 15 of uniform density inthe vicinity if the wafer 14 is being processed. The integrated device120 operates in a combined capacitive-coupled plasma (CCP) mode at itscenter and an inductively-coupled plasma (ICP) mode above the perimeterof the wafer 14, both modes being powered utilizing a common matchingnetwork 117 and RF generator 118.

The central portion 21 of the wafer support 20 and the central electrode121 of the upper electrode device 120 are similarly connected incircuits with the respective RF generators 118 and 118 through therespective corresponding matching networks 18 and 118. For example, FIG.3 illustrates an equivalent circuit for integrated device 20 in whichgenerator 17 is connected through matching network 18 to the wafersupport electrode 21, which is coupled through the plasma 15 to ground.The annular inductive portion 23 can be incorporated into this circuitin a number of ways such that the entire circuit can be brought intoresonance. The inductive portion 23 can be incorporated in series withthe support electrode 21 into the circuit at the designated location Ain FIG. 3, or in parallel with the electrode 21 at the designatedlocation B in FIG. 3. Alternatively, the inductive portion 23 can bemade part of the inductor of the matching element, shown at location Cin FIG. 3.

The ICP portions 22 and 122 can each be represented by an equivalentcircuit shown in the B box in FIG. 3. The inductor 23 or 123 is shown asthe inductance labeled L_(ANTENNA), shown connected in series between inand out impedances 24 or 124 and 25 and 125, represented by capacitiveimpedances C_(IN) and C_(OUT), respectively. This equivalent circuit canbe represented as an inductance connected in series with only one suchimpedance. C_(IN) and C_(OUT) may be either fixed or variableimpedances. Resistive components of an equivalent circuit can beconsidered as coupled to both the ICP and CCP electrodes to representthe plasma power consumption.

Typically a II-matching network of the type shown in FIG. 3 is employedto match generator and source impedance. The matching network 18 isconnected between the generator 17 and an equivalent circuit of wafersupport 21 and capacitive coupled plasma 15. The antenna of theinductive portion 23 can be connected in any of the three configurationsA, B or C in a resonant circuit with the CCP plasma and electrode 21.Similarly, the matching network 118 is connected between the generator117 and an equivalent circuit of electrode 121 and capacitive coupledplasma 15. The antenna of the inductive portion 123 can also beconnected in any of the three configurations A, B or C in a resonantcircuit with the CCP plasma and electrode 121.

Generally, three elements arranged in a T- or II-network configurationcan be used to match any discharge and inductive element impedances at agiven frequency. Another applicable matching network for an inductivedischarge element can be formed in an L-design using two variablecapacitors.

The design and construction of the matching circuits are well known to aperson skilled in the art. In general RF matching units 18 and 118 caninclude several variable reactive elements, inductors or capacitors, bywhich the impedance of the RE match section can be adjusted to achieve amatch between the RF generators 17 and 117 and RF driven electrode 21and 121 and the coil of elements 23 and 123 to thereby maximize the RFpower that is delivered to the plasma 15 within the chamber 11. Acombination of the series and parallel elements can result in thedesired impedance match of the source inductor to the driving generatorfor maximum current.

The operation and details of the device 20 and the operation and detailsof the device 120 are similar, and can be described in relation to thei-ESIC device 20, in which the chamber II pumped to a base vacuumpressure and filled with processing gas at low pressure, typically, butnot necessarily, in the range of from several mTorr to 100 mTorr. Withno plasma inside the chamber, RF power from the RF generator 18 throughmatching network 17 and capacitor 16 is delivered to the substrateholder 20. Before plasma is ignited, RF current cannot flow through thehigh impedance low-pressure gas. The substrate holder 20 is connected toan inductive element 23 in series with the impedances 24 and 25 andeventually, including stray capacitance, to ground, produces a serialresonant circuit that includes the capacitor 16 at the output of thematching network 17. Resonant frequency of such serial resonant circuitƒ is given by ƒ=1/(2π√LC), where the capacitance C in series with theinductive element 23 includes all of the capacitances of the circuit.

The inductive element 23 itself, due to stray (mutual) capacitances,represents a serial-parallel resonant circuit. Portions of the parallelcapacitive component of the parallel resonant circuit of the inductiveelement are formed from the distributed inter-winding capacitances ofthe inductive element 23, while other stray capacitance is from theelement 23 to ground. A rough estimate for a typical single helical orspiral coil (3-4 turns, diameter From 100 to 400 mm) of a type used inplasma processing gives a resonant frequency approximately in range fromabout 1 MHz to 100 MHz.

Under vacuum conditions, in the serial circuit loop the resistance isvery small (e.g. the Q-factor of such resonant circuit is very high). Atresonant conditions the impedance of inductive element 23 is high so aninduced voltage at the inductive element will be high. Because theantenna end connected to substrate holder through impedance 24 is at ahigher potential than the end connected to the ground through impedance25, an intense electric field will ignite the plasma 15 within lowpressure processing zone of the chamber 11. Generally, the matchingnetwork 17 does not need to match absolutely into the parallel resonancefrequency, because the inner end of the inductive element that isconnected through impedance 24 to central portion 21 of the wafer holder20 can strike plasma by capacitive coupling more easily than theinductively-coupled component 22. Relatively low power (<100 Watts) issufficient to ignite plasma by capacitive coupling.

Once the plasma 15 is ignited, it spreads into the volume of the chamber11 above the inductive element 22, where an intense electric fieldinduced by the RF magnetic field will deliver additional RF power intothe plasma 15. The load that the inductive element 23 now sees is muchlarger. The inductive element 23 is thereby coupled to a resistiveplasma 15. Increased resistive load in series in loop with inductiveelement 23 lowers the Q-factor of resonant circuit, which reduces thevoltage of the inductive element 23. Matching to the new resonancefrequency increases the current through inductive element 23.

Because the substrate holder 20 is exposed now to the plasma 15, RFcurrent flows through the wafer 14 and a capacitive sheath into theplasma 15, creating a parallel loop to the inductive element loop. Thiscreates a parallel resonant circuit with capacitance given by the ESC21, wafer 14 and sheath capacitances.

At constant plasma parameters, e.g. when process parameters areoptimized for unique process conditions, the choices among the inductiveelement inductance and the various capacitances may provide resonance atthe same excitation frequency as the RF supply 18. Then there would beno need for tuneable matching network. However, a high impedance RFpower supply should be used in such case or at least a load capacitorshould be used to set the impedance of the mismatched line due tovarying coil impedance at vacuum and plasma conditions, and to reduceany mismatch due to varying plasma parameters.

The inner impedance 24 may be omitted; however, at very low pressure iteliminates self-DC bias of the inductive element 23 by potential fromthe ESC 21, thus eliminating arcing. Similarly, the outer impedance 25may be omitted; however, it provides a more convenient distribution ofthe RF potential on the inductive element 23 to reduce arcingprobability.

In some special cases, for example, bifilar antenna configurations, thevalue of the stray capacitance of the inductor 23 can be designed intothe inductive element 23, as can the capacitances in and out of theinductor through impedances 24 and 25, either one or both of which canbe replaced by such stray capacitance or otherwise integrated into thedevice in the form of dielectric coatings deposited between thecapacitive substrate holder portion 21 and the inductive element 23 ofthe peripheral inductive portion 22. The thickness of these coatings andcross-sectional areas of the metallic parts at the end connectionsdefine the values of the various capacitances. Typically, the surface ofthe electrostatic chuck is coated by sprayed Alumina. Other dielectricmaterials or their combinations may be used.

Overall, several relations, which are practical and may be used as thedesign rules in the development of the I-ESIC device. The inductanceL_(ANTENNA) and parallel capacitance C_(PARALLEL) of the inductiveelement 23 should be within range C_(PARALLEL)≅β(1/ω² L_(ANTENNA)),0<β<1. The effective inductive impedance of the inductive element isthen estimated by inductance L_(EFFECTIVE ANTENNA)≅L_(ANTENNA)/(1-β),0<β<1. The relation of the capacitance in series with inductive element23 is C_(PARALLEL)≅(1-β)/(γ ω² L_(ANTENNA)), 0<β<1, 0<γ<1. Accordingly,the effective impedance of the ICP branch, L_(EFFECTIVE ICP), (theinductively-coupled portion 22 of the support 20), is within the rangeL_(EFFECTIVE ICP)≅L_(ANTENNA) (1-γ)/(1-β), 0<β<1, 0<γ<1, and theimpedance of the CCP branch, C_(CCP) (the capacitively-coupled portion21 of the support 20) is within the range C_(CCP)≅(1-β)/((1-γ) ω₂L_(ANTENNA)), 0<β<1, 0<γ<1.

In accordance with another embodiment of the invention, the RF signalfrom the matching unit 17 may be supplied to the outer end of theinductive element 23 through the impedance 25, and the inductance 23connected through impedance 24 to the substrate holder 21. In this casewhen igniting plasma, instead of a parallel resonant circuit, the serialresonant circuit will remain. However, the resonant frequency willchange due to the change in serial capacitance to the inductive element23.

Still another embodiment disclosed in this invention integrates theinductive element 23 within the matching network 17, with the inductiveelement 23 and impedances 24 and 25 replacing the coil of the matchingnetwork between the connection points of adjustable load and tuningcapacitors connected to ground (not shown). This makes a very compactintegrated ESIC.

The design and construction of the matching circuits 17 are well knownto persons skilled in the art. In general, an RF matching unit 17includes several variable reactive elements (inductors or capacitors) bywhich the impedance of the RF matching section can be adjusted toachieve a match between RF cable (or nominal RF generator output) and anRF driven electrode or coil to thereby maximize the RF power that isdelivered to the plasma 15 within the chamber 11. A combination of theseries and parallel elements can result in the desired impedance matchof the source inductor to the driving generator for maximum current.Generally, three elements can be used to match any discharge andinductive element impedances.

The inductive element 23 may have single or multiple turns that can beconnected in parallel or in series. Several examples are shown in FIGS.3A-3F, but disclosure is not limited by these only. In each of thesefigures, the wafer support 20 is shown made up of thecapacitively-coupled component or ESC 21 and the inductively-coupledcomponent 22 coupled together in series resonant circuit. Theinductively-coupled component 22 is, in turn, made up of the inductiveelement 23 coupled in the series circuit between the impedances,typically capacitances, 24 and 25. Each figure slows the matchingnetwork output connected to the ESC 21. The inductive element 23 is aplanar two-tun concentric coil in FIG. 3A, a conical concentric coil inFIG. 3B, a cylindrical or helical coil in FIG. 3C, combined concentriccoils in FIG. 3D, a two-planar concentric coil in FIG. 3E, and a bifilarconcentric coil in FIG. 3F.

One practical coil and well suited use as an inductive element 23 is theso-called bifilar configuration that can be utilized as a self-balancedinductive element due to the inter-winding stray capacitance, as shownin FIGS. 4A-4D. Geometry of the bifilar inductive element for theinductive element 23 eliminates substantially the need for theconnecting impedances 24 and 25 due to inter-winding capacitance of theindividual coils. Multiple segments each constituting full 360 degreeloops are illustrated in FIGS. 4A-4D. Partial (less-than-360 degree)loops, more-than-360 degree loops, and one or more than one loop may beemployed for the inductive element 23. The cross-section of theconductor of the inductive element 23 may be rectangular or circular orany other cross-section with typical overall diameter in range from 2 mmto 10 mm.

The inductive element 23 of the support 20 illustrated in FIG. 2 is anembodiment of a compact integrated device 20 with the inductive element23 in a form of a single three turn coil integrated into the base-plateof the ESC or central portion 21. FIG. 5A illustrates an inductiveelement 23 made of two superimposed single turn coils. FIG. 5C is asimulation of time-averaged RF electromagnetic energy and FIG. 5B is agraph of RF power density delivered into the plasma 15, both in theabsence of a Faraday shield 28. The annular distribution is typical forthe i-ESICs described herein.

FIG. 6A-6B show an inductive element 23 made of three single-turn coils,with the impedances 24 and 25 omitted for convenience. FIG. 6C is agraph of simulation results of the distribution of time-averaged RFelectromagnetic energy from and RF power density delivered into plasma15. FIG. 6D is a diagram of a Faraday shield 28 with radial slots 29. Agraph of the distribution of the RF power density through the shield ofFIG. 6D is illustrated in FIG. 6E.

FIG. 7 is a disassembled perspective view of an alternative embodimentof the wafer support of FIGS. 1 and 2 that employs a segmentedperipheral source 50 for providing the inductive element 23. Segmentedperipheral ICP sources are more particularly described in copending U.S.patent application Ser. No. 10/717,268, filed Nov. 19, 2003, by aninventor hereof, and hereby expressly incorporated by reference hereinin its entirety. The source 50 includes a segmented antenna which formsthe inductive element 23, which is mounted in a congruent insulatingplate 56 that separates the inductive device 23 from the chamber wall 12and other conductive components of the chamber 11. The element 23 hasterminals 51,52 that may respectively connect the inductor 23 in seriesbetween the impedances 24 and 25 (not shown in FIG. 7) and the ESC 21.An annular, segmented, slotted Faraday shield 53 is provided to serve asthe shield 28 over the inductor 23. An insulator 54 may be providedbetween the shield 54 and the inductor 23. Otherwise, the inductor 23 ofthe source 50 may be connected in the various ways set forth above forthe other inductor configurations. The embodiment of FIG. 7 combines thefeatures of the integrated, electrostatic, inductively-coupled wafersupport (i-ESIC) 20 and the segmented peripheral ionization source ofthe incorporated patent application.

The operation and details of the integrated element 20, in an i-ESICwafer support, can be applied to integrated element 120 in an etchsystem upper electrode. Either or both in combination contribute to thegeneration of a ring-shaped peripheral IC plasma distribution thatcombines with the central CCP to improve plasma uniformity at the wafer.

With the integrated devices 20 and 120, significant improvement can beexpected when used in ballistic electron-beam enhanced plasma etchers,where VHF radial and axial E-fields produce a spatially dependent plasmadensity due to the creation of standing waves in the space between theplanar electrodes 121 and 21, for example. Inductively coupled plasmaprovided by the integrated devices 20 and 120 will reduce plasmapotential by reducing E-fields in such systems and thereby compensatefor the standing wave profiles. Effectively higher IC plasma densitygeneration can be created even at relatively low RF powers, for example,several hundreds of Watts.

The CCP electrode(s) 21 and 121, when integrated with the inductivedevices 23, 123, respectively, create a compact RF VHF device. Theinductively coupled element 23, 123 provide increased density at theperimeters of the wafer electrode 21 and the top VHF electrode 121, thuscompensating for the radial loss of charged particles towards the wallsof the chamber, thereby generating uniform plasma density in theimmediate vicinity of the surface of the wafer being processed. Anannular slotted shield protects inductive element structure from theplasma and provides the conditions for effective inductive coupling ofan RF power into plasma. The i-ESIC device operates continuously in boththe CCP mode and the ICP mode utilizing a common matching network and RFgenerator. The CCP mode contributes to plasma that peaks in the centerof the chamber while the TCP mode contributes to plasma in a ring shapethat is distributed annularly at the perimeter of the chamber around theouter edge of the wafer.

The invention has been described in the context of exemplaryembodiments. Those skilled in the art will appreciate that additions,deletions and modifications to the features described herein may be madewithout departing from the principles of the present invention.Accordingly, the following is claimed:

1. An ICP source for a semiconductor wafer plasma etching apparatuscomprising: a substrate support electrode; a CCP electrode parallel tothe substrate support electrode; a first RF generator and matchingnetwork connected in series with the substrate support electrode; aseries RF circuit that includes a peripheral ionization source connectedto and surrounding the CCP electrode on the periphery thereof; a secondRF generator and matching network connected in series with the CCPelectrode, said RF generator coupling RF energy to the series RF circuitto bias the CCP electrode to capacitively couple energy to a plasma andto energize the peripheral ionization source to inductively coupleenergy to the plasma, to thereby form a high density plasma acrosssurface of the substrate support electrode by both capacitively andinductively coupling energy thereto from the series RF circuit.
 2. TheICP source of claim 1 wherein: the RF first generator and the second RFgenerator have different operating frequencies, the frequency of thesecond RF generator being higher than the frequency of the first RFgenerator.
 3. An ICP source for a semiconductor wafer plasma etchingapparatus comprising: a substrate support electrode; a CCP electrodeparallel to the substrate support electrode; a first RF generator andmatching network connected in series with the substrate supportelectrode; a second RF generator and matching network connected inseries with the CCP electrode; at least one series RF circuit thatincludes a peripheral ionization source connected to and surrounding oneof said electrodes on the periphery thereof, and the RF generatorcoupling RF energy to the series RF circuit to bias the electrodeincluded therein to capacitively couple energy to a plasma and toenergize the peripheral ionization source to inductively couple energyto the plasma, to thereby form a high density plasma across surface ofthe substrate support electrode by both capacitively and inductivelycoupling energy thereto from the series RF circuit.
 4. The ICP source ofclaim 3 wherein: the RF first generator and the second RF generator havedifferent operating frequencies.
 5. The ICP source of claim 3 wherein:the RF first generator and the second RF generator have differentoperating frequencies, the frequency of the second RF generator beinghigher than the frequency of the first RF generator.
 6. The ICP sourceof claim 3 wherein: the peripheral ionization source includes at leastone inductive element that generates an RF magnetic field into theplasma; and a slotted Faraday shield between the inductive element andthe plasma for facilitating the inductive coupling of energy from theinductive element into the plasma and for impeding the capacitivecoupling of energy from the inductive element to the plasma.
 7. The ICPsource of claim 3 wherein: the peripheral ionization source includes anannular inductive element that surrounds the CCP electrode.
 8. The TCPsource of claim 3 wherein: the peripheral ionization source includes anannular antenna that surrounds the CCP electrode and iscapacitively-coupled in series with the CCP electrode to form the RFseries circuit.
 9. The ICP source of claim 3 wherein: the matchingnetwork of the second RF generator and matching network is connected toan output of the second RF generator and the peripheral ionizationsource is capacitively connected at one end thereof to said matchingnetwork and is capacitively-coupled at an opposite end thereof to theCCP electrode.
 10. The ICP source of claim 3 wherein: the peripheralionization source is capacitively-coupled at one end thereof to the CCPelectrode and is capacitively-coupled at the other end thereto thechamber ground.
 11. The ICP source of claim 3 wherein: the peripheralionization source is capacitively-coupled to the CCP electrode; and thematching network of the second RF generator and matching network hasimpedances in series with the peripheral ionization source that areapproximately tuned to the frequency of the RF generator.
 12. The JCPsource of claim 3 wherein: the peripheral ionization source isconfigured to inductively couple RF energy into the plasma to form ahigh density ring-shaped plasma concentrated toward the perimeter of thesubstrate support surface.
 13. An ICP source for a semiconductor waferplasma etching apparatus comprising: a substrate support electrode; aCCP electrode parallel to the substrate support electrode; a first RFgenerator and matching network connected in series with the substratesupport electrode; a second RF generator and matching network connectedin series with the CCP electrode; a first series RKF circuit thatincludes a peripheral ionization source connected to and surrounding thesubstrate support electrode on the periphery thereof; a second series RFcircuit that includes a peripheral ionization source connected to andsurrounding the CCP electrode on the periphery thereof; and the RFgenerators coupling RF energy to the series RF circuits to bias theelectrode included therein to capacitively couple energy to a plasma andto energize the peripheral ionization source to inductively coupleenergy to the plasma, to thereby form a high density plasma acrosssurface of the substrate support electrode by both capacitively andinductively coupling energy thereto from the series RF circuit.